The present invention relates generally to a method for producing titanium alloy brazing strips and the resulting brazing strips or foil. More particularly, the invention relates to a method for using a cold-rolling process to generate a titanium based multi-layer alloy strip or foil made up of discrete layers of titanium and an additional metal or metals, such as nickel and/or copper, for example.
Brazing alloys based on titanium (Ti) are useful for brazing components that consist of titanium, nickel (Ni) and/or iron/steel (Fe) based elements or alloys, among other uses. Thin gauge brazing strips or foils have proven useful for filling braze joints, and/or for providing suitable substrate materials to form self-brazing bonds and/or for vacuum brazing. The lower melting points of common Ti-based brazing alloys cause a beneficial minimum effect on the microstructures and mechanical properties of the brazed components. Furthermore, Ti-based brazing alloys tend to provide corrosion resistance that is superior to conventional copper (Cu) or silver (Ag) based brazing alloys. A roll bonding process is useful for allowing desirable brazing alloys to be produced in continuous coil form in thin gauge. The availability of these Ti-based brazing alloys in thin foil gauge and in continuous coil lengths has been difficult to achieve as these alloys tend to be brittle and render the conventional cold working process difficult to utilize. Cold rolling titanium typically results in a brittle metal. Thus, a means for obtaining Ti based brazing alloys and/or compounds and/or laminates in a foil form using conventional cold working techniques would be useful.
In the arrangement of the components of a multi-layered brazing alloy, it would often be useful to have the Ti layer in the middle. The advantages of having the Ti layer in the middle would be the resulting uniform relative thickness of the Cu/Ni to Ti as well as the homogenous deformation of the composite during the cold reduction. These advantages are often important to provide uniform chemistry and thin finish thickness for brazing shim application.
This is in contrast to the Ti/Cuxe2x80x94Ni/Ti arrangement cited in the U.S. Pat. No. 3,652,237 (incorporated herein by reference). In that patent, the Ti layers are on the outside of the relatively soft Nixe2x80x94Cu layer. The Ti layers are hermetically welded to form an envelope to sandwich the Nixe2x80x94Cu layer. A few drawbacks can result from this arrangement. The exposed, reactive Ti layers may not permit the annealing of the composites, because it is conducted in air or hydrogen or nitrogen as Ti reacts and forms easily Ti oxide, hydride and nitride with the respective heat treating atmospheres. This leaves the annealing typically only feasible in a vacuum, which is typically not a process that can be performed in a continuous, strip-annealing manner. The hard Ti layers on top of the soft Nixe2x80x94Cu layers can also introduce non-uniform deformation of the softer layers. The non-uniform deformation of a center soft layer can affect the local alloy chemistry by deviating from the intended composition required by the brazing. This type of localized, non-uniform deformation of the center layer can also post a limit on the minimum thickness that strip can reach before the local asperity leads to a fracture of the materials.
It would be useful to have a strongly adherent, multi-layered composite produced by a roll bonding process avoiding some or all of the above problems. The roll bonding process has a few advantages over the other approaches such as plating or hot bonding. It would be advantageous to utilize a roll bonding process to provide a large reduction (such as greater than 60%, for example) during the bonding of the components in the brazing alloy. The large reduction, by breaking up the surface scale, would allow a true metallurgical bond to form between the dissimilar materials. Because the temperature of roll bonding process can be advantageously low, there is little concern of possible alloy diffusion or scale formation, especially if annealing steps can be avoided. The bond integrity could allow the composite to be processed to the desirable thickness, preferably without any intermediate annealing to soften the materials. However, using a Cuxe2x80x94Ni alloy, especially in a near-equal weight percent condition, typically results in significant hardening if utilized in a cold rolling process, and thus requires intermediate annealing steps to get to a sufficiently thin gage. A process that does not require the annealing step could provide savings in time and money.
Furthermore, intermediate annealing is often not desirable because brittle compounds between the constituent might form and render any further cold reduction difficult or even impossible. One advantage of a roll bonding process is to allow the strips to be bonded at heavy thickness, followed by the conventional cold reduction process, and thus providing a higher throughput than another process such as plating. Furthermore, the roll bonding process allows the adjustment of the relative thickness of individual constituents in order to tailor the chemical composition of brazing alloys. In addition, eliminating any annealing processes simplifies the manufacturing process and reduces energy costs. Consequently, providing a means for using a cold rolling process to generate the desired Ti alloy thin sheets and foils would be beneficial.
Provided is a brazing strip or foil comprising a first metallic layer, a second metallic layer, and a titanium layer including one of titanium and a titanium alloy. The titanium layer is placed between the first and the second metallic layers, wherein said titanium layer is roll bonded without annealing to at least one of said first and said second metallic layers.
Also provided is a brazing strip or foil comprising a first layer including one of copper, a copper alloy, nickel, and a nickel alloy; a second layer including one of copper, a copper alloy, nickel, and a nickel alloy; and a titanium layer including one of titanium and a titanium alloy. The titanium strip is placed between the first and the second metallic layers, wherein said titanium layer is roll bonded without annealing to at least one of said first and said second layers.
Further provided is a brazing strip or foil comprising a first metallic layer; a second metallic layer; a third metallic layer; a fourth metallic layer, and a titanium layer including one of titanium and a titanium alloy.
The first and the second layers are layered on one side of the titanium layer, while the third and the fourth layers layered on another side of the titanium layer.
Still further provided is a brazing strip or foil comprising a first layer including one of copper and a copper alloy; a second layer including one of nickel and a nickel alloy; a third layer including one of nickel and a nickel alloy; a fourth layer including one of copper and a copper alloy; and a titanium layer of one of elemental titanium and a titanium alloy.
The first and the second layers are layered on one side of the titanium layer, while the third and the fourth layers are layered on another side of the titanium layer, wherein said titanium layer is metallurgically bonded to at least one of said first, said second, said third, and said fourth layers.
Also provided is a brazing strip or foil comprising a titanium core of one of titanium and a titanium alloy and at least one covering layer of one of copper, a copper alloy, nickel, and a nickel alloy, with said covering layer substantially covering said titanium core, wherein said covering layer is roll bonded without annealing to said titanium core.
Additionally provided is a method of making a brazing strip or foil comprising the steps of providing a first strip including one of copper, a copper alloy, nickel, and a nickel alloy; providing a second strip including one of copper, a copper alloy, nickel, and a nickel alloy; providing a titanium strip including one of titanium and a titanium alloy; and processing the titanium strip between the first and the second strips with a rolling machine into a desired thickness, thereby resulting in a roll bonded, multi-layered brazing strip or foil.
And further provided is a method of making a brazing strip or foil comprising the steps of providing a first strip including one of copper and a copper alloy; providing a second strip including one of nickel and a nickel alloy; roll bonding the first strip to the second strip to substantially bond the first strip to the second strip and to form a reduced thickness outer composite strip
The process also involves the step of providing a titanium strip including one of titanium and a titanium alloy; and processing the titanium strip with a layer of the outer composite strip on each side of the titanium strip, the processing performed with a rolling machine to substantially bond the layers of the outer composite strip to the titanium strip and to process the resulting brazing strip or foil into a desired thickness, thereby further resulting in a thin, metallurgically bonded, multi-layered brazing strip or foil.